The present invention relates to a novel method and liquid coating composition for the formation of a silicon dioxide-based coating film on various substrates or, more particularly, relates to a method for the formation of a silica-based coating film by using a liquid coating composition having excellent storage stability and capable of giving a very dense and uniform siliceous coating film exhibiting good adhesion to the surface of the substrate on which the coating film is formed, such as semiconductor wafers, glass and ceramic plates, metal plates, plastic plates and the like, so as to be satisfactorily used for the formation of an interlayer insulating film, levelling film and protecting film on semiconductor devices and liquid crystal display panels, as a laminating material in the multilayer resist method and as a phase-shifter film as well as to a liquid coating composition therefor.
Along with the trend in the manufacturing technology of fine electronic devices such as VLSIs in recent years towards higher and higher degrees of integration, higher and higher working velocities and multiplicity of functions, the technology of multilayer circuit wiring is also under increasing requirements. While it is required in the manufacture of semiconductor devices to form a circuit pattern or an insulating layer on the surface of a substrate, for example, a difficulty in this case is that, when the substrate surface is not flat enough but has a level difference and a fine circuit pattern is to be formed on such a non-uniform surface having a level difference, a decrease is caused in the accuracy of the fine circuit pattern at the level difference so that such a substrate surface must be subjected to a treatment for surface levelling prior to the circuit patterning.
A conventional method for such a levelling treatment is the so-called spin-on-glass (SOG) method in which the substrate surface having a level difference is coated with a liquid coating composition which is a solution of a tetraalkoxy silane compound in an organic solvent mainly consisting of an alcohol so as to fill up the depressed areas at the level difference and to further provide a coating film on allover the surface followed by a heat treatment to form a silica-based or siliceous coating film.
The above described SOG method is advantageous in respect of the stability of the coating film because the film is formed from a completely inorganic siliceous material derived from the alkoxy silane compound but the method has a disadvantage that, because the coating solution has a relatively low viscosity, the thickness of the coating film formed by a single coating treatment is very limited rarely to exceed 0.4 .mu.m so that a levelling layer having a sufficiently large thickness can be obtained only by repeating a large number of times of the coating works each followed by a heat treatment sometimes resulting in the formation of cracks in the thus formed film or a decrease in the adhesion of the coating film to the substrate surface.
With an object to solve the above described problem in the prior art coating compositions for the formation of a siliceous coating film, Japanese Patent Kokai 63-241076 proposes partial replacement of the tetraalkoxy silane compound mentioned above with an alkoxy silane having at least one alkyl group directly bonded to the silicon atom in the molecule. Namely, the principal ingredient in the there disclosed coating composition is a combination of a tetraalkoxy silane with an alkyl trialkoxy silane or dialkyl dialkoxy silane subjected to a partial cohydrolysis-cocondensation reaction so that the coating composition has an adequately increased viscosity to give a thickness of 1 .mu.m or larger of the coating film formed by a single coating procedure and the coating film formed therefrom is less susceptible to crack formation by virtue of the organic groups left as bonded to the silicon atoms even after complete hydrolysis of the alkoxy silanes.
The coating film formed from the above mentioned liquid coating composition containing an alkyl-substituted alkoxy silane compound, however, has been found to have another difficult problem. While the levelling coating film formed from the coating composition is sometimes subjected to an oxygen plasma etching treatment, namely, the alkyl groups remaining in the coating film are susceptible to the attack of the oxygen plasma so that a considerable decrease in the thickness or formation of cracks is caused in the coating film by the plasma treatment although crack formation in the coating film by the oxygen plasma treatment can be prevented by an etch-back treatment necessarily leading to an increase in the manufacturing cost due to the decrease in the throughput as a consequence of the increase in the number of process steps.